For example, when a glass substrate (including a brittle material) is cut into a desired size, a cutting edge of a cutter wheel is pressed onto a surface of the brittle material with a predetermined force and is moved on the surface of the glass substrate. As a result, a scribing line is formed (hereinafter, referred to as a “scribing step”). Thereafter, a predetermined force is applied to the glass substrate along the scribing line (hereinafter, referred to as a “breaking step”). As a result, the glass substrate is cut along the scribing line.
FIG. 15 shows an example of a structure of a conventional scribing apparatus 10. The scribing apparatus 10 performs the scribing step.
The scribing apparatus 10 includes a table 11, a first guide rail 12A, a second guide rail 12B and a ball screw 13.
The table 11 is structured so as to be rotatable in a horizontal plane. A vacuum adsorption means (not shown) is provided in the table 11. The vacuum adsorption means fixes a substrate G (e.g., brittle substrate including a glass plate) mounted on the table 11 to the table 11. The first guide rail 12A and the second guide rail 12B support the table 11 such that the table 11 is movable in the Y-direction. The first guide rail 12A and the second guide rail 12B are provided in parallel to each other. The ball screw 13 moves the table 11 along the first guide rail 12A and the second guide rail 12B.
The scribing apparatus 10 further includes a first pillar 19A, a second pillar 19B, a guide bar 14, a sliding unit 15 and a motor 16.
The first pillar 19A and the second pillar 19B are vertically provided on a base of the scribing apparatus 10 having the first guide rail 12A and the second guide rail 12B interposed therebetween. The guide bar 14 is provided above the table 11 along the X-direction and constructed between the first pillar 19A and the second pillar 19B. The sliding unit 15 is provided on the guide bar 14 so as to be slidable. The motor 16 slides the sliding unit 15.
The scribing apparatus 10 further includes a scribing head 9, a motor 17 for moving the scribing head 9 upward and downward, a first CCD camera 18A and a second CCD camera 18B.
The scribing head 9 is provided in the sliding unit 15. The scribing head 9 includes a cutter wheel 29. The first CCD camera 18A and the second CCD camera 18B are provided above the guide bar 14 and detect an alignment mark formed on the substrate G.
The scribing head 9 presses the cutter wheel 29 onto the surface of the substrate G. When the motor 16 slides the sliding unit 15, the scribing head 9 moves along the guide bar 14. As a result, the cutter wheel 29 moves on the surface of the substrate G while it is being pressed onto the surface of the substrate G, and a scribing line is formed on the surface of the substrate G.
FIG. 16 shows an example of a structure of the scribing head 9. FIG. 16(a) shows a front view of the scribing head 9. FIG. 16(b) shows a bottom view of the scribing head 9.
The scribing head 9 includes a scribing head body 21, an axle bearing 22 provided in the scribing head body 21, a spindle 23 axially supported by the axle bearing 22, and a restraint axis 24 provided in the scribing head body 21 and in parallel to the spindle 23.
The scribing head 9 further includes a bearing case 25, an axle bearing 26, a turning axis 27, a cutting edge holder 28 and the cutter wheel 29. The bearing case 25 is contactable to the restraint axis 24. The axle bearing 26 is attached to the bearing case 25. The turning axis 27 is axially supported by the axle bearing 26 so as to be rotatable. The cutting edge holder 28 is turnable about the turning axis 27. The cutter wheel 29 is rotatable about a pin which is inserted at the lower end of the cutting edge holder 28. A blade 29b is formed so as to protrude in a V-shape toward the outer circumferential direction of the cutter wheel 29 (see FIG. 20). A cutting edge's ridge 29a is formed on the tip of the blade 29b (see FIG. 20).
A groove 31 having a width L is formed in the bearing case 25. A portion of the cutting edge holder 28 is embedded in the groove 31. The turning of the cutting edge holder 28 is restricted by the range of the width L of the groove 31.
The scribing head 9 further includes an energizing means 30 provided in the scribing head body 21. The energizing means 30 is, for example, an air cylinder or a servo motor. The energizing means 30 applies an energizing force to the cutter wheel 29 via the bearing case 25 and the cutting edge holder 28.
FIG. 17 shows the cutter wheel 29, the cutting edge holder 28 and the turning axis 27. An attachment position of the cutter wheel 29 with respect to the turning axis 27 will be described with reference to FIG. 16 and FIG. 17.
The cutter wheel 29 is axially supported by the cutter edge holder 28 so as to be rollable. The center of the rolling of the cutter wheel 29 is positioned away from the axial center O of the turning axis 27 by an offset distance S in a direction opposite to the movement direction of the scribing head 9.
Since the center of the rolling of the cutter wheel 29 is distant from the axial center O of the turning axis 27 by the offset distance S in a direction opposite to the movement direction of the scribing head 9, the cutter wheel 29 moves to follow the turning axis 27, which moves along with the scribing head 9 in a scribing step (hereinafter, the movement is referred to as a caster effect). The cutter wheel 29 is provided such that the axial center of turning axis 27 aligns with the movement direction of the cutter wheel 29 due to the rolling of the cutting edge's ridge 29a of the cutter wheel 29 (see FIG. 18 which is be described later).
FIG. 18 shows a positional relationship between the cutter wheel 29 and the turning axis 27 at the time of movement of the scribing head 9. Hereinafter, the caster effect will be described in further detail with reference to FIG. 16 and FIG. 18.
When the cutter wheel 29 is contacted to the substrate G in order to start the scribing step, the direction of the cutting edge's ridge 29a and the movement direction of the scribing head 9 (i.e., the movement direction of the turning axis 27) do not always align with each other. Rather, in almost all of the cases, the movement direction of the turning axis 27 and the direction of the cutting edge's ridge 29a do not coincide with each other (see FIG. 18(a) or FIG. 18(c)).
Thereafter, when the scribing head 9 moves, the direction of the cutting edge's ridge 29a is gradually changed along with the movement of the scribing head 9, and in a short amount of time, the direction of the cutting edge's ridge 29a and the movement direction of the axial center O of the turning axis 27 align with each other (FIG. 18(b)). As a result, the path of the cutter wheel 29, after the direction of the cutting edge's ridge 29a and the movement direction of the axis O of the turning axis 27 align with each other, is a straight line. Thus, the scribing line formed, by the cutter wheel 29, on the substrate is a straight line. In other words, when the direction of the cutting edge's ridge 29a of the cutter wheel 29 coincides with the axial center O of the turning axis 27, a force, which causes the cutter wheel 29 to move toward the direction where the axial center O is positioned, is generated. Such an effect is referred to as a caster effect, and the direction of the cutting edge's ridge 29a is gradually changed so as to align with the movement direction of the axial center O of the turning axis 27.
FIG. 19 shows a scribing line T, a vertical crack C and a horizontal crack D which are formed on the substrate G. FIG. 19(a) shows the scribing line T and the vertical crack C which are formed on the substrate G. FIG. 19(b) shows the vertical crack C and the horizontal crack D which are formed on the substrate G.
The scribing apparatus 10 forms the scribing line T having the continuous vertical crack C (see, for example, Reference 1). As the depth of the vertical crack C is deeper, the substrate G is more accurately broken along the scribing line T in a breaking step. As a result, the yield of the substrate improves.
When a load acting on the cutting edge of the cutter wheel 29 is larger, a deeper vertical crack C is formed. However, if the load acting on the cutting edge exceeds a predetermined magnitude, an internal distortion accumulated in the vicinity of the surface of the substrate G is saturated, a horizontal crack D occurs in a direction which is different from the forming direction of the vertical crack C. The horizontal crack D will cause a generation of a lot cullet powder and will cause a reduction of the yield of the substrate G which results from a poor quality of the cutting face of the substrate G.
FIG. 20 shows a structure of the cutter wheel 29. FIG. 20(a) is a front view of the cutter wheel 29. FIG. 20(b) is a side view of the cutter wheel 29. FIG. 20(c) is an enlarged view of a portion (portion A) of the cutter wheel 29 shown in FIG. 20(b).
The cutter wheel 29 is a disk-shaped wheel (diameter φ, width W). The cutter wheel 29 has a first side 93 and a second side 94. The blade 29b with an obtuse angle ω is formed on the outer circumference of the cutter wheel 29. The blade 29b is formed so as to protrude in a V-shape toward the outer circumferential direction of the cutter wheel 29. The cutting edge's ridge 29a is formed at the tip of the blade 29b and in the vicinity of the center of the first side 93 and the second side 94. An insertion hole 96 is formed in the vicinity of the center of the side of the cutter wheel 29.
A plurality of protrusions 81 and a plurality of grooves 95 are formed on the tip of the blade 29b. The plurality of protrusions 81 and the plurality of grooves 95 have a predetermined pitch P and a predetermined height h, respectively (see FIG. 20(c)). The plurality of protrusions 81 and the plurality of grooves 95 have a size in the order of the micrometers. Thus, they cannot be identified with the naked eye.
The cutter wheel 29 possesses an extremely high capability of forming a vertical crack which extends in the thickness direction of the substrate G. The cutter wheel 29 can form a deep vertical crack and can suppress the occurrence of a crack in horizontal direction along the surface of the substrate G.
If the vertical crack is deep enough, an accurate breaking along the scribing line can be performed in the breaking step, thereby improving the yield of the substrate G. Furthermore, the breaking step becomes easier, thereby easing or simplifying the structure of a breaking apparatus. Furthermore, it is possible to omit the breaking step.
In contrast, different from the cutter wheel 29, a protrusion or a groove is not formed on the cutting edge's ridge portion of a conventional cutter wheel. Thus, the conventional cutter wheel cannot form a vertical crack deep enough. As a result, the breaking step cannot be omitted.    Reference 1: Japanese Laid-Open Publication No. 2001-328833    Reference 2: Japanese Laid-Open Publication No. 9-188534